Using predicted movement to maintain optical-communication lock with nearby balloon

ABSTRACT

A balloon may include an optical-communication component, which may have a pointing axis. A pointing mechanism could be configured to adjust the pointing axis. The optical-communication component could be operable to communicate with a correspondent balloon via a free-space optical link. For example, the optical-communication component could include an optical receiver, transmitter, or transceiver. A controller could be configured to determine a predicted relative location of the correspondent balloon. The controller may control the pointing mechanism to adjust the pointing axis of the optical-communication component based on the predicted relative location so as to maintain the free-space optical link with the correspondent balloon.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Computing devices such as personal computers, laptop computers, tabletcomputers, cellular phones, and countless types of Internet-capabledevices are increasingly prevalent in numerous aspects of modern life.As such, the demand for data connectivity via the Internet, cellulardata networks, and other such networks, is growing. However, there aremany areas of the world where data connectivity is still unavailable, orif available, is unreliable and/or costly. Accordingly, additionalnetwork infrastructure is desirable.

SUMMARY

In a first aspect, a balloon is provided. The balloon includes anoptical-communication component. The optical-communication component hasone or more pointing axes. The optical-communication component isoperable to communicate with a correspondent balloon via a free-spaceoptical link. The optical-communication component also includes apointing mechanism configured to adjust the pointing axis. Theoptical-communication component further includes a controller. Thecontroller is configured to determine a predicted relative location ofthe correspondent balloon and control the pointing mechanism to adjustthe pointing axis based on the predicted relative location, to maintainthe free-space optical link with the correspondent balloon.

In a second aspect, a method is provided. The method includesdetermining a location of a first balloon. The first balloon includes anoptical-communication component that is configured to communicate with asecond balloon via a free-space optical link. The method additionallyincludes determining a predicted location of the second balloon relativeto the location of the first balloon based on a last known location anda last-known motion vector of the second balloon. The method alsoincludes controlling a pointing mechanism to adjust a pointing axis ofthe optical-communication component in the first balloon based on thepredicted location, to maintain the free-space optical link with thesecond balloon.

In a third aspect, a non-transitory computer readable medium havingstored instructions is provided. The instructions are executable by acomputing device to cause the computing device to perform functions. Thefunctions include: (i) determining a location of a first balloon. Thefirst balloon includes an optical-communication component that isconfigured to communicate with a second balloon via a free-space opticallink. The functions further include: (ii) determining a predictedlocation of the second balloon relative to the location of the firstballoon based on a last known location and a last known motion vector ofthe second balloon and (iii) controlling a pointing mechanism to adjusta pointing axis of the optical-communication component in the firstballoon based on the predicted location, to maintain the free-spaceoptical link with the second balloon.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating a balloon network,according to an example embodiment.

FIG. 2 is a block diagram illustrating a balloon-network control system,according to an example embodiment.

FIG. 3 is a simplified block diagram illustrating a high-altitudeballoon, according to an example embodiment.

FIG. 4 shows a balloon network that includes super-nodes and sub-nodes,according to an example embodiment.

FIG. 5 is a simplified block diagram illustrating an optical transmitterand an optical receiver, according to an example embodiment.

FIG. 6 shows a balloon communication scenario, according to an exampleembodiment.

FIG. 7 is a method, according to an example embodiment.

DETAILED DESCRIPTION

Example methods and systems are described herein. Any example embodimentor feature described herein is not necessarily to be construed aspreferred or advantageous over other embodiments or features. Theexample embodiments described herein are not meant to be limiting. Itwill be readily understood that certain aspects of the disclosed systemsand methods can be arranged and combined in a wide variety of differentconfigurations, all of which are contemplated herein.

Furthermore, the particular arrangements shown in the Figures should notbe viewed as limiting. It should be understood that other embodimentsmay include more or less of each element shown in a given Figure.Further, some of the illustrated elements may be combined or omitted.Yet further, an example embodiment may include elements that are notillustrated in the Figures.

1. Overview

Example embodiments help to provide a data network that includes aplurality of balloons; for example, a mesh network formed byhigh-altitude balloons deployed in the stratosphere. Since winds in thestratosphere may affect the locations of the balloons in a differentialmanner, each balloon in an example network may be configured to changeits horizontal position by adjusting its vertical position (i.e.,altitude). For instance, by adjusting its altitude, a balloon may beable find winds that will carry it horizontally (e.g., latitudinallyand/or longitudinally) to a desired horizontal location.

Further, in an example balloon network, the balloons may communicatewith one another using free-space optical communications. For instance,the balloons may be configured for optical communications usingultra-bright LEDs (which are also referred to as “high-power” or“high-output” LEDs). In some instances, lasers could be used instead ofor in addition to LEDs, although regulations for laser communicationsmay restrict laser usage. In addition, the balloons may communicate withground-based station(s) using radio-frequency (RF) communications.

In some embodiments, a high-altitude-balloon network may be homogenous.That is, the balloons in a high-altitude-balloon network could besubstantially similar to each other in one or more ways. Morespecifically, in a homogenous high-altitude-balloon network, eachballoon is configured to communicate with one or more other balloons viafree-space optical links. Further, some or all of the balloons in such anetwork, may additionally be configured to communicate with ground-basedand/or satellite-based station(s) using RF and/or opticalcommunications. Thus, in some embodiments, the balloons may behomogenous in so far as each balloon is configured for free-spaceoptical communication with other balloons, but heterogeneous with regardto RF communications with ground-based stations.

In other embodiments, a high-altitude-balloon network may beheterogeneous, and thus may include two or more different types ofballoons. For example, some balloons in a heterogeneous network may beconfigured as super-nodes, while other balloons may be configured assub-nodes. It is also possible that some balloons in a heterogeneousnetwork may be configured to function as both a super-node and asub-node. Such balloons may function as either a super-node or asub-node at a particular time, or, alternatively, act as bothsimultaneously depending on the context. For instance, an exampleballoon could aggregate search requests of a first type to transmit to aground-based station. The example balloon could also send searchrequests of a second type to another balloon, which could act as asuper-node in that context. Further, some balloons, which may besuper-nodes in an example embodiment, can be configured to communicatevia optical links with ground-based stations and/or satellites.

In an example configuration, the super-node balloons may be configuredto communicate with nearby super-node balloons via free-space opticallinks. However, the sub-node balloons may not be configured forfree-space optical communication, and may instead be configured for someother type of communication, such as RF communications. In that case, asuper-node may be further configured to communicate with sub-nodes usingRF communications. Thus, the sub-nodes may relay communications betweenthe super-nodes and one or more ground-based stations using RFcommunications. In this way, the super-nodes may collectively functionas backhaul for the balloon network, while the sub-nodes function torelay communications from the super-nodes to ground-based stations.

The present disclosure describes various example embodiments ofapparatuses, methods, and functions executable by a computer-readablemedium that are generally operable to maintain an optical communicationslink between a first balloon and a second balloon based on a predictedlocation of the second balloon relative to the first balloon.

In one example embodiment, a balloon includes an optical-communicationcomponent with a pointing axis. The optical-communication componentcould include an optical receiver, an optical transmitter, and/or anoptical transceiver. The pointing axis can be adjusted in order tomaintain a free-space optical link with a correspondent balloon.

For example, the balloon could include a pointing mechanism configuredto adjust the pointing axis of the optical-communication component.Additionally, the balloon could include a controller. The controllercould be configured to determine a predicted relative location of thecorrespondent balloon. The predicted relative location of thecorrespondent balloon could be determined using a Kalman filter methodor other similar algorithms for doing inference and prediction in adynamic system. Furthermore, the controller may control the pointingmechanism to adjust the pointing axis based on the predicted relativelocation so as to maintain the free-space optical link with thecorrespondent balloon.

2. Example Balloon Networks

FIG. 1 is a simplified block diagram illustrating a balloon network 100,according to an example embodiment. As shown, balloon network 100includes balloons 102A to 102F, which are configured to communicate withone another via free-space optical links 104. Balloons 102A to 102Fcould additionally or alternatively be configured to communicate withone another via RF links 114. Balloons 102A to 102F may collectivelyfunction as a mesh network for packet-data communications. Further, atleast some of balloons 102A and 102B may be configured for RFcommunications with ground-based stations 106 and 112 via respective RFlinks 108. Further, some balloons, such as balloon 102F, could beconfigured to communicate via optical link 110 with ground-based station112.

In an example embodiment, balloons 102A to 102F are high-altitudeballoons, which are deployed in the stratosphere. At moderate latitudes,the stratosphere includes altitudes between approximately 10 kilometers(km) and 50 km altitude above the surface. At the poles, thestratosphere starts at an altitude of approximately 8 km. In an exampleembodiment, high-altitude balloons may be generally configured tooperate in an altitude range within the stratosphere that has relativelylow wind speed (e.g., between 5 and 20 miles per hour (mph)).

More specifically, in a high-altitude-balloon network, balloons 102A to102F may generally be configured to operate at altitudes between 18 kmand 25 km (although other altitudes are possible). This altitude rangemay be advantageous for several reasons. In particular, this layer ofthe stratosphere generally has relatively low wind speeds (e.g., windsbetween 5 and 20 mph) and relatively little turbulence. Further, whilethe winds between 18 km and 25 km may vary with latitude and by season,the variations can be modeled in a reasonably accurate manner.Additionally, altitudes above 18 km are typically above the maximumflight level designated for commercial air traffic. Therefore,interference with commercial flights is not a concern when balloons aredeployed between 18 km and 25 km.

To transmit data to another balloon, a given balloon 102A to 102F may beconfigured to transmit an optical signal via an optical link 104. In anexample embodiment, a given balloon 102A to 102F may use one or morehigh-power light-emitting diodes (LEDs) to transmit an optical signal.Alternatively, some or all of balloons 102A to 102F may include lasersystems for free-space optical communications over optical links 104.Other types of free-space optical communication are possible. Further,in order to receive an optical signal from another balloon via anoptical link 104, a given balloon 102A to 102F may include one or moreoptical receivers. Additional details of example balloons are discussedin greater detail below, with reference to FIG. 3.

In a further aspect, balloons 102A to 102F may utilize one or more ofvarious different RF air-interface protocols for communication withground-based stations 106 and 112 via respective RF links 108. Forinstance, some or all of balloons 102A to 102F may be configured tocommunicate with ground-based stations 106 and 112 using protocolsdescribed in IEEE 802.11 (including any of the IEEE 802.11 revisions),various cellular protocols such as GSM, CDMA, UMTS, EV-DO, WiMAX, and/orLTE, and/or one or more propriety protocols developed for balloon-groundRF communication, among other possibilities.

In a further aspect, there may be scenarios where RF links 108 do notprovide a desired link capacity for balloon-to-ground communications.For instance, increased capacity may be desirable to provide backhaullinks from a ground-based gateway, and in other scenarios as well.Accordingly, an example network may also include downlink balloons,which could provide a high-capacity air-ground link.

For example, in balloon network 100, balloon 102F is configured as adownlink balloon. Like other balloons in an example network, a downlinkballoon 102F may be operable for optical communication with otherballoons via optical links 104. However, a downlink balloon 102F mayalso be configured for free-space optical communication with aground-based station 112 via an optical link 110. Optical link 110 maytherefore serve as a high-capacity link (as compared to an RF link 108)between the balloon network 100 and the ground-based station 112.

Note that in some implementations, a downlink balloon 102F mayadditionally be operable for RF communication with ground-based stations106. In other cases, a downlink balloon 102F may only use an opticallink for balloon-to-ground communications. Further, while thearrangement shown in FIG. 1 includes just one downlink balloon 102F, anexample balloon network can also include multiple downlink balloons. Onthe other hand, a balloon network can also be implemented without anydownlink balloons.

In other implementations, a downlink balloon may be equipped with aspecialized, high-bandwidth RF communication system forballoon-to-ground communications, instead of, or in addition to, afree-space optical communication system. The high-bandwidth RFcommunication system may take the form of an ultra-wideband system,which may provide an RF link with substantially the same capacity as oneof the optical links 104. Other forms are also possible.

Ground-based stations, such as ground-based stations 106 and/or 112, maytake various forms. Generally, a ground-based station may includecomponents such as transceivers, transmitters, and/or receivers forcommunication via RF links and/or optical links with a balloon network.Further, a ground-based station may use various air-interface protocolsin order to communicate with a balloon 102A to 102F over an RF link 108.As such, ground-based stations 106 and 112 may be configured as anaccess point via which various devices can connect to balloon network100. Ground-based stations 106 and 112 may have other configurationsand/or serve other purposes without departing from the scope of theinvention.

In a further aspect, some or all of balloons 102A to 102F could beconfigured to establish a communication link with space-based satellitesin addition to, or as an alternative to, a ground-based communicationlink. In some embodiments, a balloon may communicate with a satellitevia an optical link. However, other types of satellite communicationsare possible.

Further, some ground-based stations, such as ground-based stations 106and 112, may be configured as gateways between balloon network 100 andone or more other networks. Such ground-based stations 106 and 112 maythus serve as an interface between the balloon network and the Internet,a cellular service provider's network, and/or other types of networks.Variations on this configuration and other configurations ofground-based stations 106 and 112 are also possible.

2a) Mesh Network Functionality

As noted, balloons 102A to 102F may collectively function as a meshnetwork. More specifically, since balloons 102A to 102F may communicatewith one another using free-space optical links, the balloons maycollectively function as a free-space optical mesh network.

In a mesh-network configuration, each balloon 102A to 102F may functionas a node of the mesh network, which is operable to receive datadirected to it and to route data to other balloons. As such, data may berouted from a source balloon to a destination balloon by determining anappropriate sequence of optical links between the source balloon and thedestination balloon. These optical links may be collectively referred toas a “lightpath” for the connection between the source and destinationballoons. Further, each of the optical links may be referred to as a“hop” on the lightpath.

To operate as a mesh network, balloons 102A to 102F may employ variousrouting techniques and self-healing algorithms. In some embodiments, aballoon network 100 may employ adaptive or dynamic routing, where alightpath between a source and destination balloon is determined andset-up when the connection is needed, and released at a later time.Further, when adaptive routing is used, the lightpath may be determineddynamically depending upon the current state, past state, and/orpredicted state of the balloon network.

In addition, the network topology may change as the balloons 102A to102F move relative to one another and/or relative to the ground.Accordingly, an example balloon network 100 may apply a mesh protocol toupdate the state of the network as the topology of the network changes.For example, to address the mobility of the balloons 102A to 102F,balloon network 100 may employ and/or adapt various techniques that areemployed in mobile ad hoc networks (MANETs). Other examples are possibleas well.

In some implementations, a balloon network 100 may be configured as atransparent mesh network. More specifically, in a transparent balloonnetwork, the balloons may include components for physical switching thatis entirely optical, without any electrical components involved in thephysical routing of optical signals. Thus, in a transparentconfiguration with optical switching, signals travel through a multi-hoplightpath that is entirely optical.

In other implementations, the balloon network 100 may implement afree-space optical mesh network that is opaque. In an opaqueconfiguration, some or all balloons 102A to 102F may implementoptical-electrical-optical (OEO) switching. For example, some or allballoons may include optical cross-connects (OXCs) for OEO conversion ofoptical signals. Other opaque configurations are also possible.Additionally, network configurations are possible that include routingpaths with both transparent and opaque sections.

In a further aspect, balloons in an example balloon network 100 mayimplement wavelength division multiplexing (WDM), which may help toincrease link capacity. When WDM is implemented with transparentswitching, physical lightpaths through the balloon network may besubject to the “wavelength continuity constraint.” More specifically,because the switching in a transparent network is entirely optical, itmay be necessary to assign the same wavelength for all optical links ona given lightpath.

An opaque configuration, on the other hand, may avoid the wavelengthcontinuity constraint. In particular, balloons in an opaque balloonnetwork may include the OEO switching systems operable for wavelengthconversion. As a result, balloons can convert the wavelength of anoptical signal at each hop along a lightpath. Alternatively, opticalwavelength conversion could take place at only selected hops along thelightpath.

Further, various routing algorithms may be employed in an opaqueconfiguration. For example, to determine a primary lightpath and/or oneor more diverse backup lightpaths for a given connection, exampleballoons may apply or consider shortest-path routing techniques such asDijkstra's algorithm and k-shortest path, and/or edge and node-diverseor disjoint routing such as Suurballe's algorithm, among others.Additionally or alternatively, techniques for maintaining a particularquality of service (QoS) may be employed when determining a lightpath.Other techniques are also possible.

2b) Station-Keeping Functionality

In an example embodiment, a balloon network 100 may implementstation-keeping functions to help provide a desired network topology.For example, station-keeping may involve each balloon 102A to 102Fmaintaining and/or moving into a certain position relative to one ormore other balloons in the network (and possibly in a certain positionrelative to the ground). As part of this process, each balloon 102A to102F may implement station-keeping functions to determine its desiredpositioning within the desired topology, and if necessary, to determinehow to move to the desired position.

The desired topology may vary depending upon the particularimplementation. In some cases, balloons may implement station-keeping toprovide a substantially uniform topology. In such cases, a given balloon102A to 102F may implement station-keeping functions to position itselfat substantially the same distance (or within a certain range ofdistances) from adjacent balloons in the balloon network 100.

In other cases, a balloon network 100 may have a non-uniform topology.For instance, example embodiments may involve topologies where balloonsare distributed more or less densely in certain areas, for variousreasons. As an example, to help meet the higher bandwidth demands thatare typical in urban areas, balloons may be clustered more densely overurban areas. For similar reasons, the distribution of balloons may bedenser over land than over large bodies of water. Many other examples ofnon-uniform topologies are possible.

In a further aspect, the topology of an example balloon network may beadaptable. In particular, station-keeping functionality of exampleballoons may allow the balloons to adjust their respective positioningin accordance with a change in the desired topology of the network. Forexample, one or more balloons could move to new positions to increase ordecrease the density of balloons in a given area. Other examples arepossible.

In some embodiments, a balloon network 100 may employ an energy functionto determine if and/or how balloons should move to provide a desiredtopology. In particular, the state of a given balloon and the states ofsome or all nearby balloons may be input to an energy function. Theenergy function may apply the current states of the given balloon andthe nearby balloons to a desired network state (e.g., a statecorresponding to the desired topology). A vector indicating a desiredmovement of the given balloon may then be determined by determining thegradient of the energy function. The given balloon may then determineappropriate actions to take in order to effectuate the desired movement.For example, a balloon may determine an altitude adjustment oradjustments such that winds will move the balloon in the desired manner.

2c) Control of Balloons in a Balloon Network

In some embodiments, mesh networking and/or station-keeping functionsmay be centralized. For example, FIG. 2 is a block diagram illustratinga balloon-network control system, according to an example embodiment. Inparticular, FIG. 2 shows a distributed control system, which includes acentral control system 200 and a number of regional control-systems 202Ato 202B. Such a control system may be configured to coordinate certainfunctionality for balloon network 204, and as such, may be configured tocontrol and/or coordinate certain functions for balloons 206A to 206I.

In the illustrated embodiment, central control system 200 may beconfigured to communicate with balloons 206A to 206I via a number ofregional control systems 202A to 202C. These regional control systems202A to 202C may be configured to receive communications and/oraggregate data from balloons in the respective geographic areas thatthey cover, and to relay the communications and/or data to centralcontrol system 200. Further, regional control systems 202A to 202C maybe configured to route communications from central control system 200 tothe balloons in their respective geographic areas. For instance, asshown in FIG. 2, regional control system 202A may relay communicationsand/or data between balloons 206A to 206C and central control system200, regional control system 202B may relay communications and/or databetween balloons 206D to 206F and central control system 200, andregional control system 202C may relay communications and/or databetween balloons 206G to 206I and central control system 200.

In order to facilitate communications between the central control system200 and balloons 206A to 206I, certain balloons may be configured asdownlink balloons, which are operable to communicate with regionalcontrol systems 202A to 202C. Accordingly, each regional control system202A to 202C may be configured to communicate with the downlink balloonor balloons in the respective geographic area it covers. For example, inthe illustrated embodiment, balloons 206A, 206F, and 206I are configuredas downlink balloons. As such, regional control systems 202A to 202C mayrespectively communicate with balloons 206A, 206F, and 206I via opticallinks 206, 208, and 210, respectively.

In the illustrated configuration, only some of balloons 206A to 206I areconfigured as downlink balloons. The balloons 206A, 206F, and 206I thatare configured as downlink balloons may relay communications fromcentral control system 200 to other balloons in the balloon network,such as balloons 206B to 206E, 206G, and 206H. However, it should beunderstood that in some implementations, it is possible that allballoons may function as downlink balloons. Further, while FIG. 2 showsmultiple balloons configured as downlink balloons, it is also possiblefor a balloon network to include only one downlink balloon, or possiblyeven no downlink balloons.

Note that a regional control system 202A to 202C may in fact just be aparticular type of ground-based station that is configured tocommunicate with downlink balloons (e.g., such as ground-based station112 of FIG. 1). Thus, while not shown in FIG. 2, a control system may beimplemented in conjunction with other types of ground-based stations(e.g., access points, gateways, etc.).

In a centralized control arrangement, such as that shown in FIG. 2, thecentral control system 200 (and possibly regional control systems 202Ato 202C as well) may coordinate certain mesh-networking functions forballoon network 204. For example, balloons 206A to 206I may send thecentral control system 200 certain state information, which the centralcontrol system 200 may utilize to determine the state of balloon network204. The state information from a given balloon may include locationdata, optical-link information (e.g., the identity of other balloonswith which the balloon has established an optical link, the bandwidth ofthe link, wavelength usage and/or availability on a link, etc.), winddata collected by the balloon, and/or other types of information.Accordingly, the central control system 200 may aggregate stateinformation from some or all of the balloons 206A to 206I in order todetermine an overall state of the network.

The overall state of the network may then be used to coordinate and/orfacilitate certain mesh-networking functions such as determininglightpaths for connections. For example, the central control system 200may determine a current topology based on the aggregate stateinformation from some or all of the balloons 206A to 206I. The topologymay provide a picture of the current optical links that are available inballoon network and/or the wavelength availability on the links. Thistopology may then be sent to some or all of the balloons so that arouting technique may be employed to select appropriate lightpaths (andpossibly backup lightpaths) for communications through the balloonnetwork 204.

In a further aspect, the central control system 200 (and possiblyregional control systems 202A to 202C as well) may also coordinatecertain station-keeping functions for balloon network 204. For example,the central control system 200 may input state information that isreceived from balloons 206A to 206I to an energy function, which mayeffectively compare the current topology of the network to a desiredtopology, and provide a vector indicating a direction of movement (ifany) for each balloon, such that the balloons can move towards thedesired topology. Further, the central control system 200 may usealtitudinal wind data to determine respective altitude adjustments thatmay be initiated to achieve the movement towards the desired topology.The central control system 200 may provide and/or support otherstation-keeping functions as well.

FIG. 2 shows a distributed arrangement that provides centralizedcontrol, with regional control systems 202A to 202C coordinatingcommunications between a central control system 200 and a balloonnetwork 204. Such an arrangement may be useful to provide centralizedcontrol for a balloon network that covers a large geographic area. Insome embodiments, a distributed arrangement may even support a globalballoon network that provides coverage everywhere on earth. Of course, adistributed-control arrangement may be useful in other scenarios aswell.

Further, it should be understood that other control-system arrangementsare also possible. For instance, some implementations may involve acentralized control system with additional layers (e.g., sub-regionsystems within the regional control systems, and so on). Alternatively,control functions may be provided by a single, centralized, controlsystem, which communicates directly with one or more downlink balloons.

In some embodiments, control and coordination of a balloon network maybe shared by a ground-based control system and a balloon network tovarying degrees, depending upon the implementation. In fact, in someembodiments, there may be no ground-based control systems. In such anembodiment, all network control and coordination functions may beimplemented by the balloon network itself. For example, certain balloonsmay be configured to provide the same or similar functions as centralcontrol system 200 and/or regional control systems 202A to 202C. Otherexamples are also possible.

Furthermore, control and/or coordination of a balloon network may bede-centralized. For example, each balloon may relay state informationto, and receive state information from, some or all nearby balloons.Further, each balloon may relay state information that it receives froma nearby balloon to some or all nearby balloons. When all balloons doso, each balloon may be able to individually determine the state of thenetwork. Alternatively, certain balloons may be designated to aggregatestate information for a given portion of the network. These balloons maythen coordinate with one another to determine the overall state of thenetwork.

Further, in some aspects, control of a balloon network may be partiallyor entirely localized, such that it is not dependent on the overallstate of the network. For example, individual balloons may implementstation-keeping functions that only consider nearby balloons. Inparticular, each balloon may implement an energy function that takesinto account its own state and the states of nearby balloons. The energyfunction may be used to maintain and/or move to a desired position withrespect to the nearby balloons, without necessarily considering thedesired topology of the network as a whole. However, when each balloonimplements such an energy function for station-keeping, the balloonnetwork as a whole may maintain and/or move towards the desiredtopology.

As an example, each balloon A may receive distance information d₁ tod_(k) with respect to each of its k closest neighbors. Each balloon Amay treat the distance to each of the k balloons as a virtual springwith vector representing a force direction from the first nearestneighbor balloon i toward balloon A and with force magnitudeproportional to d_(i). The balloon A may sum each of the k vectors andthe summed vector is the vector of desired movement for balloon A.Balloon A may attempt to achieve the desired movement by controlling itsaltitude.

Alternatively, this process could assign the force magnitude of each ofthese virtual forces equal to d_(i)×d_(i), for instance. Otheralgorithms for assigning force magnitudes for respective balloons in amesh network are possible.

In another embodiment, a similar process could be carried out for eachof the k balloons and each balloon could transmit its planned movementvector to its local neighbors. Further rounds of refinement to eachballoon's planned movement vector can be made based on the correspondingplanned movement vectors of its neighbors. It will be evident to thoseskilled in the art that other algorithms could be implemented in aballoon network in an effort to maintain a set of balloon spacingsand/or a specific network capacity level over a given geographiclocation.

2d) Example Balloon Configuration

Various types of balloon systems may be incorporated in an exampleballoon network. As noted above, an example embodiment may utilizehigh-altitude balloons, which could typically operate in an altituderange between 18 km and 25 km. FIG. 3 shows a high-altitude balloon 300,according to an example embodiment. As shown, the balloon 300 includesan envelope 302, a skirt 304, a payload 306, and a cut-down system 308,which is attached between the balloon 302 and payload 304.

The envelope 302 and skirt 304 may take various forms, which may becurrently well-known or yet to be developed. For instance, the envelope302 and/or skirt 304 may be made of materials including metalized Mylaror BoPet. Additionally or alternatively, some or all of the envelope 302and/or skirt 304 may be constructed from a highly-flexible latexmaterial or a rubber material such as chloroprene. Other materials arealso possible. Further, the shape and size of the envelope 302 and skirt304 may vary depending upon the particular implementation. Additionally,the envelope 302 may be filled with various different types of gases,such as helium and/or hydrogen. Other types of gases are possible aswell.

The payload 306 of balloon 300 may include a processor 312 and on-boarddata storage, such as memory 314. The memory 314 may take the form of orinclude a non-transitory computer-readable medium. The non-transitorycomputer-readable medium may have instructions stored thereon, which canbe accessed and executed by the processor 312 in order to carry out theballoon functions described herein. Thus, processor 312, in conjunctionwith instructions stored in memory 314, and/or other components, mayfunction as a controller of balloon 300.

The payload 306 of balloon 300 may also include various other types ofequipment and systems to provide a number of different functions. Forexample, payload 306 may include an optical communication system 316,which may transmit optical signals via an ultra-bright LED system 320,and which may receive optical signals via an optical-communicationreceiver 322 (e.g., a photodiode receiver system). Further, payload 306may include an RF communication system 318, which may transmit and/orreceive RF communications via an antenna system 340.

The payload 306 may also include a power supply 326 to supply power tothe various components of balloon 300. The power supply 326 couldinclude a rechargeable battery. In other embodiments, the power supply326 may additionally or alternatively represent other means known in theart for producing power. In addition, the balloon 300 may include asolar power generation system 327. The solar power generation system 327may include solar panels and could be used to generate power thatcharges and/or is distributed by the power supply 326.

The payload 306 may additionally include a positioning system 324. Thepositioning system 324 could include, for example, a global positioningsystem (GPS), an inertial navigation system, and/or a star-trackingsystem. The positioning system 324 may additionally or alternativelyinclude various motion sensors (e.g., accelerometers, magnetometers,gyroscopes, and/or compasses).

The positioning system 324 may additionally or alternatively include oneor more video and/or still cameras, and/or various sensors for capturingenvironmental data.

Some or all of the components and systems within payload 306 may beimplemented in a radiosonde or other probe, which may be operable tomeasure, e.g., pressure, altitude, geographical position (latitude andlongitude), temperature, relative humidity, and/or wind speed and/orwind direction, among other information.

As noted, balloon 300 includes an ultra-bright LED system 320 forfree-space optical communication with other balloons. As such, opticalcommunication system 316 may be configured to transmit a free-spaceoptical signal by modulating the ultra-bright LED system 320. Theoptical communication system 316 may be implemented with mechanicalsystems and/or with hardware, firmware, and/or software. Generally, themanner in which an optical communication system is implemented may vary,depending upon the particular application. The optical communicationsystem 316 and other associated components are described in furtherdetail below.

In a further aspect, balloon 300 may be configured for altitude control.For instance, balloon 300 may include a variable buoyancy system, whichis configured to change the altitude of the balloon 300 by adjusting thevolume and/or density of the gas in the balloon 300. A variable buoyancysystem may take various forms, and may generally be any system that canchange the volume and/or density of gas in the envelope 302.

In an example embodiment, a variable buoyancy system may include abladder 310 that is located inside of envelope 302. The bladder 310could be an elastic chamber configured to hold liquid and/or gas.Alternatively, the bladder 310 need not be inside the envelope 302. Forinstance, the bladder 310 could be a rigid bladder that could bepressurized well beyond neutral pressure. The buoyancy of the balloon300 may therefore be adjusted by changing the density and/or volume ofthe gas in bladder 310. To change the density in bladder 310, balloon300 may be configured with systems and/or mechanisms for heating and/orcooling the gas in bladder 310. Further, to change the volume, balloon300 may include pumps or other features for adding gas to and/orremoving gas from bladder 310. Additionally or alternatively, to changethe volume of bladder 310, balloon 300 may include release valves orother features that are controllable to allow gas to escape from bladder310. Multiple bladders 310 could be implemented within the scope of thisdisclosure. For instance, multiple bladders could be used to improveballoon stability.

In an example embodiment, the envelope 302 could be filled with helium,hydrogen or other lighter-than-air material. The envelope 302 could thushave an associated upward buoyancy force. In such an embodiment, air inthe bladder 310 could be considered a ballast tank that may have anassociated downward ballast force. In another example embodiment, theamount of air in the bladder 310 could be changed by pumping air (e.g.,with an air compressor) into and out of the bladder 310. By adjustingthe amount of air in the bladder 310, the ballast force may becontrolled. In some embodiments, the ballast force may be used, in part,to counteract the buoyancy force and/or to provide altitude stability.

In other embodiments, the envelope 302 could be substantially rigid andinclude an enclosed volume. Air could be evacuated from envelope 302while the enclosed volume is substantially maintained. In other words,at least a partial vacuum could be created and maintained within theenclosed volume. Thus, the envelope 302 and the enclosed volume couldbecome lighter than air and provide a buoyancy force. In yet otherembodiments, air or another material could be controllably introducedinto the partial vacuum of the enclosed volume in an effort to adjustthe overall buoyancy force and/or to provide altitude control.

In another embodiment, a portion of the envelope 302 could be a firstcolor (e.g., black) and/or a first material from the rest of envelope302, which may have a second color (e.g., white) and/or a secondmaterial. For instance, the first color and/or first material could beconfigured to absorb a relatively larger amount of solar energy than thesecond color and/or second material. Thus, rotating the balloon suchthat the first material is facing the sun may act to heat the envelope302 as well as the gas inside the envelope 302. In this way, thebuoyancy force of the envelope 302 may increase. By rotating the balloonsuch that the second material is facing the sun, the temperature of gasinside the envelope 302 may decrease. Accordingly, the buoyancy forcemay decrease. In this manner, the buoyancy force of the balloon could beadjusted by changing the temperature/volume of gas inside the envelope302 using solar energy. In such embodiments, it is possible that abladder 310 may not be a necessary element of balloon 300. Thus, invarious contemplated embodiments, altitude control of balloon 300 couldbe achieved, at least in part, by adjusting the rotation of the balloonwith respect to the sun.

Further, a balloon 306 may include a navigation system (not shown). Thenavigation system may implement station-keeping functions to maintainposition within and/or move to a position in accordance with a desiredtopology. In particular, the navigation system may use altitudinal winddata to determine altitudinal adjustments that result in the windcarrying the balloon in a desired direction and/or to a desiredlocation. The altitude-control system may then make adjustments to thedensity of the balloon chamber in order to effectuate the determinedaltitudinal adjustments and cause the balloon to move laterally to thedesired direction and/or to the desired location. Alternatively, thealtitudinal adjustments may be computed by a ground-based orsatellite-based control system and communicated to the high-altitudeballoon. In other embodiments, specific balloons in a heterogeneousballoon network may be configured to compute altitudinal adjustments forother balloons and transmit the adjustment commands to those otherballoons.

As shown, the balloon 300 also includes a cut-down system 308. Thecut-down system 308 may be activated to separate the payload 306 fromthe rest of balloon 300. The cut-down system 308 could include at leasta connector, such as a balloon cord, connecting the payload 306 to theenvelope 302 and a means for severing the connector (e.g., a shearingmechanism or an explosive bolt). In an example embodiment, the ballooncord, which may be nylon, is wrapped with a nichrome wire. A currentcould be passed through the nichrome wire to heat it and melt the cord,cutting the payload 306 away from the envelope 302.

The cut-down functionality may be utilized anytime the payload needs tobe accessed on the ground, such as when it is time to remove balloon 300from a balloon network, when maintenance is due on systems withinpayload 306, and/or when power supply 326 needs to be recharged orreplaced.

In an alternative arrangement, a balloon may not include a cut-downsystem. In such an arrangement, the navigation system may be operable tonavigate the balloon to a landing location, in the event the balloonneeds to be removed from the network and/or accessed on the ground.Further, it is possible that a balloon may be self-sustaining, such thatit does not need to be accessed on the ground. In yet other embodiments,in-flight balloons may be serviced by specific service balloons oranother type of service aerostat or service aircraft.

3. Balloon Network with Optical and RF Links Between Balloons

In some embodiments, a high-altitude-balloon network may includesuper-node balloons, which communicate with one another via opticallinks, as well as sub-node balloons, which communicate with super-nodeballoons via RF links. Generally, the optical links between super-nodeballoons may be configured to have more bandwidth than the RF linksbetween super-node and sub-node balloons. As such, the super-nodeballoons may function as the backbone of the balloon network, while thesub-nodes may provide sub-networks providing access to the balloonnetwork and/or connecting the balloon network to other networks.

FIG. 4 is a simplified block diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an example embodiment.More specifically, FIG. 4 illustrates a portion of a balloon network 400that includes super-node balloons 410A to 410C (which may also bereferred to as “super-nodes”) and sub-node balloons 420 (which may alsobe referred to as “sub-nodes”).

Each super-node balloon 410A to 410C may include a free-space opticalcommunication system that is operable for packet-data communication withother super-node balloons. As such, super-nodes may communicate with oneanother over optical links. For example, in the illustrated embodiment,super-node 410A and super-node 401B may communicate with one anotherover optical link 402, and super-node 410A and super-node 401C maycommunicate with one another over optical link 404.

Each of the sub-node balloons 420 may include a radio-frequency (RF)communication system that is operable for packet-data communication overone or more RF air interfaces. Accordingly, each super-node balloon 410Ato 410C may include an RF communication system that is operable to routepacket data to one or more nearby sub-node balloons 420. When a sub-node420 receives packet data from a super-node 410, the sub-node 420 may useits RF communication system to route the packet data to a ground-basedstation 430 via an RF air interface.

As noted above, the super-nodes 410A to 410C may be configured for bothlonger-range optical communication with other super-nodes andshorter-range RF communications with nearby sub-nodes 420. For example,super-nodes 410A to 410C may use using high-power or ultra-bright LEDsto transmit optical signals over optical links 402, 404, which mayextend for as much as 100 miles, or possibly more. Configured as such,the super-nodes 410A to 410C may be capable of optical communications atdata rates of 10 to 50 GBit/sec or more.

A larger number of high-altitude balloons may then be configured assub-nodes, which may communicate with ground-based Internet nodes atdata rates on the order of approximately 10 Mbit/sec. For instance, inthe illustrated implementation, the sub-nodes 420 may be configured toconnect the super-nodes 410 to other networks and/or directly to clientdevices.

Note that the data speeds and link distances described in the aboveexample and elsewhere herein are provided for illustrative purposes andshould not be considered limiting; other data speeds and link distancesare possible.

In some embodiments, the super-nodes 410A to 410C may function as a corenetwork, while the sub-nodes 420 function as one or more access networksto the core network. In such an embodiment, some or all of the sub-nodes420 may also function as gateways to the balloon network 400.Additionally or alternatively, some or all of ground-based stations 430may function as gateways to the balloon network 400.

4. A balloon with an Optical-Communication Component Having a PointingAxis Adjustable Based on a Predicted Relative Location of aCorrespondent Balloon

A balloon (e.g., a first balloon) may be configured to communicate witha correspondent balloon (e.g., a second balloon), for example tomaintain an optical-communications link between the balloons. The twoballoons could be similar, or the two balloons could be dissimilar(e.g., different types of nodes in a heterogeneous balloon network). Insome embodiments, an optical-communications link may be additionallyestablished between the balloon to a ground-based station and/or aspace-based platform (e.g., a satellite).

The balloon could include one or more optical-communication components,such as an optical transmitter, an optical receiver, and/or an opticaltransceiver. Accordingly, some example embodiments could be described inreference to FIG. 3 and FIG. 5. FIG. 5 is a simplified block diagramillustrating an optical transmitter 500 and an optical receiver 520,according to an example embodiment.

In such an example embodiment, an optical transmitter 500 could receivedata in 502 that could be in the form of electrical and/or opticalsignals. The electrical and/or optical signals that comprise the data in502 may include information in the form of one or more digital or analogvoltage and/or optical intensity level(s). The data in 502 could bereceived by the optical transmitter 500 via an electrical (e.g., wire ormulti-conductor cable) or optical (e.g., optical fiber or waveguide)connection. Modulator 504 could encode the information from the data in502 using one or more encoding techniques, such as intensity modulation,phase modulation, pulse-wave modulation, and/or frequency modulation.Those skilled in the art will understand that modulator 504 couldreasonably use other known encoding schemes.

A driver 506 may convert the encoded information into a driving signalthat could act to illuminate a light source 508. In an exampleembodiment, light source 508 could represent one or more light-emittingdiodes (LED) or lasers. The light source 508 could also include otherhigh-power light sources known in the art. The emission wavelengths oflight source 508 could be in the ultraviolet, visible, infrared andmicrowave spectral regimes. The wavelength band of emission could berelatively narrow (e.g., a few nanometers in spectral width).Alternatively, the wavelength band could be broadband (e.g., a largeportion of visible spectrum, as is common in ‘white’ LED emission).Further, light source 508 could be configured to emit light at multiplediscrete wavelengths (e.g., with a two-color laser) or within multiplewavebands (e.g., with a multi-color LED).

The light source 508 could be configured to modulate (e.g., turn on andoff) at high frequencies in order to achieve more than 10gigabit-per-second (GBit/s) data throughput. Light emitted from lightsource 508 could be either collimated or uncollimated. Further, theintensity of the emitted light could be adjustable. The emitted lightcould be collimated and/or focused by transmission optics 510. Thetransmission optics 510 could include elements such as a telescopeand/or a beam expander. Depending upon the embodiment, other opticalelements could be included in the transmission optics 510, such as thoseknown in the art that may be used for long-range imaging.

In an alternative embodiment, light emitted from the light source 508could be modulated by a modulator. For instance, a polarizationmodulator could be configured to modulate the polarization of the lightemitted from light source 508. In such a scenario, the free-spaceoptical signal could include data based, at least in part, on thepolarization of light. Various modulator types are possible, including aliquid-crystal modulator and a spatial light modulator, among others. Inpractice, the free-space optical signal could include more than one typeof light modulation. Further, the light modulation could be performed athigh frequencies to achieve more than 10 GBit/s data transmission.

Depending upon the embodiment, the elements of the transmission optics510 could be configured in different ways in an effort to efficientlytransmit output light as a free-space optical signal, such as signal512, to a correspondent balloon. For instance, the transmission optics510 could be configured to provide an optical-communications link overseveral kilometers. In other embodiments, the transmission optics 510could be configured differently in order to establish anoptical-communications link with a ground-based station or a space-basedplatform. For instance, the configuration of optical components in thetransmission optics 510 could be different if the intended target was aground-based station (15-30 km away) compared to if the intended targetwas a space-based platform (geosynchronous orbits can be over 42,000km). Therefore, the distance between the balloon and a space-basedtarget could be over 42,000 km away. Accordingly, the optical componentsin the transmission optics 510 could be adjusted (e.g., by using a zoomand/or focusing feature on the telescope). In other embodiments,separate sets of transmission optics 510 could be used based upon, forinstance, the intended target distance and target altitude.

An optical receiver 520 could be configured to receive a signal 522 thatcould represent part of an optical-communications link. The signal 522could be a free-space optical signal with encoded information from acorrespondent balloon or another airborne platform. The signal 522 couldalso originate from a ground-based station or a space-based platform(e.g., a satellite or other space-craft).

Signal 522 could be optically collected by receiver optics 524. Receiveroptics 524 could include a telescope or any combination of optics (suchas refractive lenses and reflective mirrors) known in the art forreceiving free-space optical signals at long distances (e.g., more thanseveral kilometers). Light received by the receiver optics 524 could beamplified using an optical preamplifier 526. The optical preamplifier526 could include one or more of a doped fiber amplifier, semiconductoroptical amplifier (SOA), Raman amplifier, and/or a parametric amplifier.Other optical amplifier types are possible within the context of thisdisclosure.

The amplified optical signal could be filtered by an optical filter 528.In some embodiments, the optical filter could include an absorptivefilter, an interference filter, and/or a dichroic filter. The opticalsignal could be filtered in various ways, for instance based uponwavelength (e.g., in a bandpass filter) and/or polarization (e.g., witha polarizer or waveplate).

The filtered light could be detected by a photodetector 530. Thephotodetector 530 could include one or more photodiodes, charge-coupleddevices (CCD), photoconductors, or other means for photon-sensing knownin the art. The photodetector 530 could include a multiple elementdetector system configured to detect changes in an optical beamlocation. In an example embodiment, the photodetector could transduceincident light into a photocurrent signal. The photocurrent signal couldthen be amplified with a transimpedance amplifier 532. Thetransimpedance amplifier 532 may be configured to convert thephotocurrent signal into a voltage and provide signal gain. Otheramplifier types are possible, and could be dependent, for instance, uponthe output type of the photodetector. For instance, if the photodetector530 is a photoconductive device that produces a photovoltage, atranconductance amplifier could be used to convert the photovoltage to asignal current. Those skilled in the art will understand that there aremany other ways to convert a photosignal into an electrical signal, andthose other ways are contemplated herein.

The optical receiver could also include a demodulator/error-correctionelement 534, which may be configured to extract information from thesignal 522. The type of demodulation utilized by thedemodulator/error-correction element 534 may depend upon the type ofmodulation initially performed on the optical signal. For instance, thedemodulation method may include carrier recovery, clock recovery, framesynchronization, pulse compression, error detection and correction,and/or mixing with a local oscillator (e.g., heterodyne detection).Other demodulation methods known in the field of optical and digitalsignal processing are possible.

The demodulator/error-correction element 534 could be further configuredto detect and correct errors in the as-received signal. For instance,the element 534 could include a hash function, a checksum algorithm,and/or other redundancy check algorithms in an effort to reduce datatransmission errors. Further, error-correcting codes (ECCs) (e.g., Turboor low-density parity-check codes) could be implemented in thedemodulator/error-correction element 534 to detect and correct errors.If errors are found, the optical receiver 520 could be configured tocorrect the error automatically with a forward error correction (FEC)algorithm. Alternatively, the optical receiver 520 could be configuredto send an automatic repeat request (ARQ) to the transmitting node via areverse channel in an effort to get a new transmission of the data.

In reference to FIG. 3, the optical-communication component(s) 330, suchas optical transmitter 500 and/or optical receiver 520, could bemechanically and/or optically coupled to a gimbal mount 328. The gimbalmount 328 could be configured to adjustably point in a pointingdirection 332. Second optical-communication component(s) 336 could bemechanically and/or optically coupled to a gimbal mount 334 and orientedalong a pointing direction 338. The second optical-communicationcomponent(s) 336 could represent multiple components configured tomaintain optical communication links with multiple nodes and/or nodes atvarying altitudes. For instance, optical-communication component 330could be configured to maintain an optical link with a neighboringballoon while optical-communication component 336 could be configured tomaintain an optical link with a ground-based station. In other words,one or more optical-communication components could be used withrespective pointing mechanisms in an effort to maintain optical linkswith one or more ground-, air-, or space-based network nodes. Within thecontext of this disclosure, the optical-communication components 330 and336 may include an optical transmitter, an optical receiver, and/or anoptical transceiver.

FIG. 6 shows an example scenario 600 for maintaining a free-spaceoptical communication link between balloons. In this example, a balloon602 attempts to maintain a free-space optical link with a correspondentballoon (depicted in FIG. 6 as Balloon 2). Each of the correspondentballoon locations 610A-C could represent the location of an examplecorrespondent balloon at time A, B, and C. The balloon 602 may have apointing mechanism, such as gimbal mount 328. The pointing mechanismcould adjust a pointing axis of an optical-communication component. Theoptical-communication component could be an optical receiver, an opticaltransmitter, and/or an optical transceiver.

The balloon 602 could further include a controller. The controller couldbe any combination of positioning systems, computers, and memory. Otherconfigurations of the controller are possible. The controller could beconfigured to determine a predicted location of the correspondentballoon at time B and subsequently at time C, which could be representedby predicted balloon locations 620B and 620C, respectively. Thecontroller could determine the predicted location in various ways.

In one example embodiment, the controller could acquire a firstlocation, which could be the location of the balloon itself Althoughballoon 602 is illustrated as at one location, it is understood thatwithin the context of the disclosure that the balloon 602 could alsomove and all other locations and motion vectors could be determined withrespect to the instantaneous location and velocity of balloon 602.

The controller could also acquire a last-known location of thecorrespondent balloon and optionally, a last-known motion vector of thecorrespondent balloon. The last-known location of the correspondentballoon could include GPS and/or inertial navigation system informationabout a location of the correspondent balloon at a specific time. Forinstance, correspondent balloon location 610A could represent thelocation (e.g., longitude, latitude, and altitude) of the correspondentballoon at time A. Correspondent balloon location 610B could representthe location of the correspondent balloon at time B, and so on.

The last-known motion vector of the correspondent balloon could include,for instance, the direction, velocity, and/or acceleration of thecorrespondent balloon at a given time. For example, motion vectors 612and 614 could represent the direction, velocity, and/or acceleration ofthe correspondent balloons at time A and time B, respectively.

The last-known location and, optionally, the last known motion vector ofthe correspondent balloon could be acquired via a RF link or othercommunication link. For instance, a correspondent balloon at location610A could transmit its last known location (e.g., GPS coordinatesand/or inertial navigation data) to the balloon 602 at time A. Further,a motion vector 612 could represent velocity, heading, and/oracceleration data from the correspondent balloon.

The controller could use the last-known location and, optionally, thelast-known motion vector as inputs to a Kalman filter that could outputa predicted relative location of the correspondent balloon. Kalmanfilters are described in further detail below. The predicted relativelocation determination could take into account, for instance, therelative latitude/longitude of the respective balloons (602 and 610A-C),as well as their respective altitudes. Actual paths 611 and 613 couldrepresent the actual path of the balloon from time A through time C. Theactual correspondent balloon location and the predicted relativelocation are depicted as visibly separated in FIG. 6 for visual anddescriptive clarity only. In one embodiment, the Kalman method could beperformed many times per second. Thus, in practice, the actual andpredicted locations of the correspondent balloon may be sufficientlyclose so as to maintain the free-space optical link throughout scenario600.

The controller may control the pointing mechanism to adjust the pointingaxis based on the predicted relative location. For instance, thecontroller could adjust the pointing direction 332 on the gimbal mount328 (located on the first balloon) to move from an initial axis 604towards a first predicted target axis 606 in an effort to track thecorrespondent balloon and to maintain the free-space opticalcommunication link between the respective balloons.

At time B, the process could be repeated by the controller. For example,the controller could receive the GPS coordinates of the correspondentballoon at location 610B. Further, the controller could receive othersensor data that may suggest a motion vector 614. The combination ofthese data could produce a subsequent predicted relative location 620Cof the correspondent balloon at time C, which may differ from the actualposition of the correspondent balloon 610C at time C. Accordingly, thecontroller could control the pointing direction 332 on the gimbal mount328 to move from the first predicted target axis 606 to a secondpredicted target axis 608 so as to maintain the free-space optical linkbetween the respective balloons.

In one embodiment, the optical-communication component may be an opticalreceiver. In such a case, the pointing mechanism could be controlled bythe controller to adjust the pointing axis of the optical receivertowards a predicted target axis in an effort to maintain an opticalcommunications link. Further to maintain the communications link, theoutput of the optical receiver may be monitored to detect the free-spaceoptical signal from the correspondent balloon 610A-C. In one exampleembodiment, a multi-element detector system (e.g., a quadraturedetector) could be used to optimize the pointing axis of the pointingmechanism. For instance, a beam misalignment condition may be determinedif one of the detector elements of the multi-element detector systemreceives more signal than the others. In such a case, the pointing axiscould be controlled by the controller to equalize the output from eachof the detector elements in an effort to realign the transmitted beamwith the detector system. Alternatively or additionally, the pointingaxis could be controlled to maximize the overall output signal from thedetector system. Additionally, the output signal from the detectorsignal could be used as an input to the aforementioned Kalman filtermethod.

In another embodiment, the optical-communication component on the firstballoon could be an optical transmitter. As described above, thepointing mechanism could be controlled by the controller to adjust thepointing axis of the optical transmitter towards a predicted target axisin an effort to maintain an optical communications link. Thecorrespondent balloon 610A-C could transmit information to the firstballoon via a reverse channel. The transmitted information could includethe GPS location and/or inertial guidance data of the correspondentballoon. The transmitted information could also represent beampositioning information. For instance, the correspondent balloon couldinclude a multi-element detector system operable to optimize opticalbeam alignment. Output from the multi-element detector could betransmitted to the first balloon and used as input to the Kalman filteror other sensor fusion algorithm. A reverse channel could be representedby any means with which the correspondent balloon 610A-C could signalthe balloon 602, (e.g., an RF signal, an optical signal, or an indirectlink through a ground-based station). Upon receiving the transmittedinformation from the correspondent balloon 610A-C and determining a newpredicted relative location of the correspondent balloon, the controllercould control the pointing axis of the optical transmitter so as tomaintain the free-space optical link.

In further embodiments, a reverse channel may not be necessary tomaintain the free-space optical link. For instance, a camera on theballoon 602 may provide images that could be used as feedback during theballoon-tracking process. As such, the controller may control thepointing mechanism to adjust the pointing axis such that thecorrespondent balloon 610A-C is centered within the images. Thus, afree-space optical link may be sufficiently maintained if thecorrespondent balloon 610A-C is centered within such images.

In yet another embodiment, the optical-communication component couldinclude an optical transceiver. The optical transceiver may represent anoptical receiver and an optical transmitter having a shared pointingaxis. The optical transceiver could thus be configured to send andreceive optical signals along the shared pointing axis. As describedabove, the pointing mechanism could be controlled by the controller toadjust the pointing axis of the optical transceiver in an effort tomaintain an optical communications link. In such an example embodiment,the optical transceiver could i) receive data from the correspondentballoon, ii) transmit data to the correspondent balloon, or both.Accordingly, upon receiving location data about the correspondentballoon direction via the free-space optical link and/or another reversechannel, a Kalman filter method could be used to determine a predictedrelative location of the second balloon. The pointing axis could beadjusted so as to point at the predicted relative location of the secondballoon and thus maintain the optical communication link.

5. Method for Controlling a Pointing Mechanism to Adjust a Pointing Axisof an Optical-Communication Component in a First Balloon Based on aPredicted Location of a Second Balloon

A method 700 is provided for pointing an optical-communication componentattached to a first balloon towards a second balloon based on apredicted location of the second balloon relative to the first balloon.The method could be performed using any of the apparatus shown in FIGS.1-6 and described above. However, other configurations could be used.FIG. 7 illustrates the steps in an example method with reference to FIG.6, however, it is understood that in other embodiments, the steps mayappear in different order and steps could be added or subtracted.

Step 702 includes determining a location of a first balloon 602. Thefirst balloon 602 may include an optical-communications componentconfigured to communicate with a second balloon (610A-C) via afree-space optical link.

Step 704 includes determining a predicted location 620B&C of a secondballoon relative to the location of the first balloon 602. The predictedlocation 620B&C could be based on a last known location and a last knownmotion vector of the second balloon 610A-C. The predicted location620B&C could be determined, in one example embodiment, using a Kalmanfilter method. The Kalman filter method could use as inputs varioussensor data (e.g., GPS data, inertial navigation data, camera images,etc.) so as to determine the predicted locations.

The Kalman filter may include an algorithm that incorporates the sensordata with a physical model of the balloon and its environment, whichcould include neighboring balloons. The algorithm could determine theprevious state of the system and incorporate the previous state withcurrent state sensor data to predict a current state of the system. Thesystem state predictions from the Kalman filter method may typically bemore accurate than, for instance, utilizing data from only one sensor(e.g., predicting a current balloon position by extrapolating balloonGPS data).

In the example embodiment involving the Kalman filter method, the secondballoon could have an on-board GPS receiver. The GPS receiver couldprovide an estimate of the second balloon's position. However, the GPSestimate of the second balloon's position may include noise, jitter, andgenerally imperfect location data. The second balloon may transmit theGPS coordinates as well as sensor measurements from other sources, suchas an accelerometer, gyroscope, and/or other sensors, to the firstballoon. Upon receiving at least a portion of the GPS data and othersensor measurements, the Kalman filter method could be carried out in arecurring cycle. The cycle could repeat multiple times per second or ata different rate. The cycle could alternatively or additionally betriggered by an external event, for instance by the first balloonestablishing an optical communication link with the second balloon.Other triggers are possible. The Kalman filter cycle could involve twomain phases (e.g., a prediction phase and an update phase).

In the prediction phase, the first balloon could predict the secondballoon's current position using the physical model of the secondballoon and its environment plus any perturbations to other systemvariables, for instance, wind velocity, heading, and acceleration.Additionally, a covariance (a measure of how much two random variables,such as wind velocity and balloon position, change together) related tothe predicted position could be calculated. For instance, the covariancecould be proportional to the speed of the second balloon.

In the update phase, the first balloon could receive GPS positioningdata relating the position of the second balloon. The positioning datacould be used to update the initial predicted position to obtain anupdated position.

The predicted and updated positions could be used as inputs and weightedbased on their associated covariances. The output of the Kalman filtermethod could provide a predicted relative location of the secondballoon. The predicted relative location of the second balloon could bethus used to adjust the pointing angle of the optical-communicationdevice so as to maintain a free-space optical link between the firstballoon and the second balloon.

As described above, the Kalman filter method could be performed in thefirst balloon by a computing system that could include acomputer-readable medium, a processor, and a memory. Furthermore, theKalman filter method could be performed in both the first and the secondballoons in an effort to correct the alignment of the respectiveoptical-communication components operable in the free-space opticallink. In yet another embodiment, one of the communicating balloons couldperform the method on behalf of both balloons, control its on-boardoptical-communication component as well as transmit a control command tothe other balloon in order to remotely adjust the other balloon'soptical-communication component.

Alternatively, the Kalman filter method could be carried out in part orwholly by a computing system located on another air-, ground-, orspace-based platform. For example, the predicted location of the secondballoon could be determined by a super-node balloon in the balloonnetwork. The method could also be carried out by a distributed networkof processors, such as a server network.

It will be understood to those skilled in the art that various otherembodiments involving different sensor and data fusion algorithms arepossible in determining a predicted location and those other embodimentsare contemplated herein. For instance, other linear quadratic estimation(LQE) and/or dynamic positioning algorithms known in the art of controltheory may be reasonably applied within the context of this disclosure.

Step 706 includes controlling a pointing mechanism to adjust a pointingaxis of an optical-communication component in the first balloon 602based on the predicted location 620B & 620C. The optical-communicationcomponent in the first balloon 602 is operable to communicate with thesecond balloon 610A-C via a free-space optical link, and may include anoptical receiver, an optical transmitter, and/or an optical transceiver.

With reference to FIG. 3, the gimbal mount 328, which may also be termedthe pointing mechanism, could be controlled to point theoptical-communication component 330 towards a predicted target axis 606& 608.

The controlling of the pointing mechanism could be performed by thefirst balloon, for instance using processor 312 and memory 314 tocontrol the gimbal mount 328. Alternatively, the pointing mechanismcould be controlled remotely by another balloon or ground- orspace-based station.

Once under local or remote control, the pointing mechanism could beadjusted to point along the predicted target axis 606 & 608. In otherwords, adjustments could be performed with an effort to maintain afree-space optical link between the first and the second balloon. In oneembodiment, if the optical-communication component is an opticalreceiver, the pointing mechanism may be adjusted so that the opticalreceiver is moved to the predicted target axis 606 & 608. The pointingmechanism may also adjust the pointing axis continuously so as to tracka moving target axis (e.g., due to a moving balloon). The rate and/oramount of pointing axis adjustment could be based on the rate of changeof the predicted target axis. Other techniques known in the art tomaintain a line-of-sight optical link may be reasonably used within thecontext of the disclosure.

6. A Non-Transitory Computer Readable Medium with Instructions toControl a Pointing Mechanism to Adjust a Pointing Axis of anOptical-Communication Component in a First Balloon Based on a PredictedLocation of a Second Balloon

Some or all of the functions described above and illustrated in FIGS. 3,5, 6, and 7 may be performed by a computing device in response to theexecution of instructions stored in a non-transitory computer readablemedium. The non-transitory computer readable medium could be, forexample, a random access memory (RAM), a read-only memory (ROM), a flashmemory, a cache memory, one or more magnetically encoded discs, one ormore optically encoded discs, or any other form of non-transitory datastorage. The non-transitory computer readable medium could also bedistributed among multiple data storage elements, which could beremotely located from each other. The computing device that executes thestored instructions could be a computing device, such as the processor312 illustrated in FIG. 3. Alternatively, the computing device thatexecutes the stored instructions could be another computing device, suchas a server in a server network, or a ground-based station.

The non-transitory computer readable medium may store instructionsexecutable by the processor 312 to perform various functions. Thefunctions could include the determination of a location of a firstballoon. The first balloon could include an optical-communicationcomponent that is configured to communicate with a second balloon via afree-space optical link. The functions could further include determininga predicted location of the second balloon relative to the location ofthe first balloon. The determination of the predicted location could bebased on a last-known location and a last-known motion vector of thesecond balloon.

The determination of the predicted location could use various sensorfusion algorithms, including, but not limited to a Kalman filter method.Other algorithms are possible.

The non-transitory computer readable medium may include furtherfunctions such as controlling a pointing mechanism to adjust a pointingaxis of an optical-communication component in the first balloon based onthe predicted location to maintain a free-space optical link with thesecond balloon.

CONCLUSION

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. While various aspects and embodiments have beendisclosed herein, other aspects and embodiments will be apparent tothose skilled in the art. The various aspects and embodiments disclosedherein are for purposes of illustration and are not intended to belimiting, with the true scope and spirit being indicated by thefollowing claims.

1. A balloon, comprising: an optical-communication component having apointing axis, wherein the optical-communication component comprises anoptical receiver configured to receive free-space optical signals alongthe pointing axis, wherein the optical-communication component isoperable to communicate with a correspondent balloon via a free-spaceoptical link, and wherein the optical receiver comprises a multipleelement detector system configured to detect changes in an optical beamlocation; a pointing mechanism configured to adjust the pointing axis; acontroller, wherein the controller is configured to determine apredicted relative location of the correspondent balloon and control thepointing mechanism to adjust the pointing axis based on the predictedrelative location, to maintain the free-space optical link with thecorrespondent balloon.
 2. The balloon of claim 1, wherein the balloon isa high-altitude balloon in a high-altitude balloon mesh network. 3.(canceled)
 4. The balloon of claim 1, wherein the optical receivercomprises a photodiode.
 5. (canceled)
 6. The balloon of claim 1, whereinthe controller is configured to determine the predicted relativelocation of the correspondent balloon based on free-space opticalsignals from the correspondent balloon received by the optical receiver.7. The balloon of claim 1, wherein the optical-communication componentfurther comprises an optical transmitter configured to transmitfree-space optical signals along the pointing axis.
 8. The balloon ofclaim 1, wherein the optical transmitter comprises a light-emittingdiode.
 9. The balloon of claim 1, wherein the optical transmittercomprises a laser.
 10. The balloon of claim 1, wherein the opticaltransmitter comprises a modulator, wherein the modulator is configuredto modulate light to form the free-space optical signals.
 11. Theballoon of claim 10, wherein the modulator comprises a spatial lightmodulator.
 12. The balloon of claim 10, wherein the modulator comprisesa polarization modulator.
 13. The balloon of claim 10, wherein themodulator comprises a liquid-crystal modulator.
 14. (canceled)
 15. Theballoon of claim 1, wherein the controller is configured to determinethe predicted relative location of the correspondent balloon based on aKalman filter method.
 16. The balloon of claim 15, wherein the predictedrelative location of the correspondent balloon is determined using alast known location of the correspondent balloon as an input to theKalman filter method.
 17. The balloon of claim 15, wherein the predictedrelative location of the correspondent balloon is determined using alast known location and a last known motion vector of the correspondentballoon as inputs to the Kalman filter method.
 18. The balloon of claim1, wherein the controller is configured to determine the predictedrelative location of the correspondent balloon based on alinear-quadratic estimation method.
 19. The balloon of claim 1, furthercomprising a camera configured to acquire images of the correspondentballoon, wherein the controller is configured to determine the predictedrelative location of the correspondent balloon based on the images. 20.The balloon of claim 1, further comprising a radio transceiverconfigured to acquire radio signals from the correspondent balloon,wherein the controller is configured to determine the predicted relativelocation of the correspondent balloon based on the radio signals. 21.The balloon of claim 1, further comprising a global positioning systemconfigured to acquire global positioning system data, wherein thecontroller is configured to determine the predicted relative location ofthe correspondent balloon based on the global positioning system data.22. The balloon of claim 1, further comprising an inertial guidancesystem configured to acquire inertial guidance system data, wherein thecontroller is configured to determine the predicted relative location ofthe correspondent balloon based on the inertial guidance system data.23. A method, comprising: determining a location of a first balloon,wherein the first balloon comprises an optical-communication componenthaving a pointing axis, wherein the optical communication component isconfigured to communicate with a second balloon via a free-space opticallink, wherein the optical communication component comprises an opticalreceiver configured to receive free-space optical signals along thepointing axis, and wherein the optical receiver comprises a multipleelement detector system configured to detect changes in an optical beamlocation; determining a predicted location of the second balloonrelative to the location of the first balloon based on a last knownlocation and a last known motion vector of the second balloon; andcontrolling a pointing mechanism to adjust the pointing axis of theoptical-communication component in the first balloon based on thepredicted location, to maintain the free-space optical link with thesecond balloon.
 24. The method of claim 23, wherein determining thepredicted location of the second balloon comprises using a Kalman filtermethod.
 25. The method of claim 24, wherein determining the predictedlocation of the second balloon comprises using the last known locationof the second balloon as an input to the Kalman filter method.
 26. Themethod of claim 24, wherein determining the predicted location of thesecond balloon comprises using the last known location and the lastknown motion vector of the second balloon as inputs to the Kalman filtermethod.
 27. The method of claim 23, wherein determining the predictedlocation of the second balloon comprises using a linear-quadraticestimation method.
 28. (canceled)
 29. The method of claim 23, whereinthe optical-communication component further comprises an opticaltransmitter configured to transmit free-space optical signals along thepointing axis.
 30. (canceled)
 31. A non-transitory computer readablemedium having stored therein instructions executable by a computingdevice to cause the computing device to perform functions comprising:determining a location of a first balloon, wherein the first ballooncomprises an optical communication component having a pointing axis,wherein the optical communication component is configured to communicatewith a second balloon via a free-space optical link, wherein the opticalcommunication component comprises an optical receiver configured toreceive free-space optical signals along the pointing axis, and whereinthe optical receiver comprises a multiple element detector systemconfigured to detect changes in an optical beam location; determining apredicted location of the second balloon relative to the location of thefirst balloon based on a last known location and a last known motionvector of the second balloon; and controlling a pointing mechanism toadjust the pointing axis of an optical-communication component in thefirst balloon based on the predicted location, to maintain thefree-space optical link with the second balloon.
 32. The non-transitorycomputer readable medium of claim 31, wherein determining the predictedlocation of the second balloon comprises using a Kalman filter method.33. The non-transitory computer readable medium of claim 32, whereindetermining the predicted location of the second balloon comprises usingthe last known location and the last known motion vector of the secondballoon as inputs to the Kalman filter method.
 34. The non-transitorycomputer readable medium of claim 31, wherein determining the predictedlocation of the second balloon comprises using a linear-quadraticestimation method.